| Title | Developing High-Temperature Functional Microcapsules for Delayed Flow Diverter Formation in EGS Reservoirs |
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| Authors | Chun CHANG, Seiji NAKAGAWA, Oscar SANDOVAL, William KIBIKAS, Timothy KNEAFSEY, Patrick DOBSON, Abraham SAMUEL, Michael OTTO, Stephen BRUCE, Carlos RODRIGUEZ, Nils KAARGESON-LOE, Robert Banker COMER |
| Year | 2024 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Enhanced Geothermal System; Fracture permeability manipulation; Flow diverter; Microcapsules; Microfluidics |
| Abstract | During Enhanced Geothermal System development, subsurface permeability is enhanced via stimulation processes that re-open pre-existing fractures, create new ones, or achieve a combination of both. Because of the heterogeneous nature of fractures, some fractures or portions of a fracture will take more flow than others, leading to fast fluid flow and a rapid decline of heat production. While near-wellbore fluid flow management has been widely investigated, controlling the reservoir permeability away from wells is challenging, as injected materials need to form solid plugs only after they reach the target locations. To control the timing of the flow-diverter formation in high temperature conditions, we are developing a technology to deliver one or more components of the diverter-forming chemicals in microcapsules with a thin polymer shell. The material properties of the shell are designed so that it can withstand moderately high temperatures (up to 200˚C) of the injected fluid for a short period of time (up to 1 hour), but thermally degrades and releases the reactants at higher reservoir temperatures. A microfluidic system has been developed that can continuously produce reactant-encapsulating particles. The diameter of the produced particles is in the range of ~250-650 μm, which can be controlled by using capillary tubes with different diameters and by adjusting the flow rates of the encapsulated fluid and the UV-curable epoxy resin for the shell. Laboratory experiments have demonstrated that (1) microcapsules containing chemical activators can be produced at different sizes and geometries, (2) the durability of the shell can be produced and tuned to satisfy different conditions, and (3) the microcapsules release their contents at high-temperatures, thus achieving their intended role in activator release and flow-diverter formation. SAND2023-10370A. |